Abstract:
The one-dimensional framework used by traditional one-dimensional LSMs (including the Mosaic LSM) is not amenable to an adequate treatment of runoff generation or subsurface soil moisture movement, since both processes in nature are largely controlled by spatial heterogeneity in soil moisture. Consider, for example, that many LSMs coupled to AGCMs effectively consider soil ... moisture to be spatially uniform in thin soil layers (in some cases a few centimeters thick) that span hundreds of kilometers! Calculations of soil moisture transport between these massively extensive but very thin layers are then computed with precise equations developed for use at the point scale. Needless to say, nature does not work this way.

This deficiency suggests a logical development path, namely, an improved treatment of the subgrid horizontal structure of land surface hydrological processes. The development of the NSIPP Catchment LSM is an attempt to follow this path. In this LSM, subgrid heterogeneity in surface moisture state is treated statistically, since computational constraints (now and in the foreseeable future) prevent it s explicit resolution. Nevertheless, the applied distributions are related sensibly to the topography, which exerts a major control over much of the subgrid variability.